Implementation of Robotic Shoulder Complex actuated by Pneumatic Artificial Muscles

The shoulder complex is known as the highest degrees-of-freedom (DoFs) mechanism in the human body. It consists of the clavicle, scapula, and thorax allowing the human arm to perform a large range of motion. However, in the case of robotic systems, the shoulder complex is often kinematically simplified or substituted with a serial-chain mechanism due to the complexity of the musculoskeletal systems. As a matter of fact, the human shoulder makes use of the scapula movement to extend its range of motion. The pneumatic artificial muscles (PAMs) have been evaluated as the most similar actuators to the human muscles. When pressurized air is applied, PAMs swell and contract. PAMs are faster and more lightweight than other actuators because the power source is air. Also, PAMs are appealing as small-sized air compressors are becoming available. This paper presents a robotic shoulder complex actuated by PAMs. The PAMs are arranged in such a way as to mimic the musculoskeletal system of the shoulder complex. In order to allow a lightweight implementation of the robotic shoulder complex, ball joints and a deformable membrane are chosen instead of mechanical bearings. The effectiveness of the proposed mechanism was validated through simulation and experiments.